The following references to and descriptions of prior proposals or products are not intended to be and are not to be construed as statements or admissions of common general knowledge in the art. In particular, the following prior art discussion does not relate to what is commonly or well known by the person skilled in the art, but may assist in the understanding of the inventiveness of the present invention, of which the identification of pertinent prior proposals is but one part.
Rising prices paid by consumers for electricity supply is an issue of concern to many householders. There is also world-wide disquiet about the use of fossil fuels for electricity generation. There is concern that such use is wasteful of a non-renewable resource, and also that such use generates carbon dioxide emissions which may contribute to global warming.
In response to these concerns, electricity generation equipment has been installed in many domestic and business premises. Such electricity generation installations have included wind generation and various forms of cogeneration, with the most common being solar electricity generation, in particular roof-mounted solar photovoltaic (PV) generation equipment.
The output of a solar generation installation varies with the availability of solar radiation. Time of day, time of year and weather conditions affect the available solar radiation and hence the level of electricity generated by the solar installation.
The demand for electricity by a household also varies depending on what appliances are in use, and the degree of use of the appliances.
This combined variability means that at some times, the solar generation installation will be able to generate more electricity than the current household demand, while at other times, the household demand will exceed the level of electrical power available from the installation.
When the household demand exceeds the solar supply, electrical energy is drawn from the grid. Conversely, when the solar supply exceeds household demand, the energy utility which provides the grid may allow the household to supply, or “feed-in”, electricity to the grid. The energy utility may pay for this generated electricity either directly or by rebate from the consumer's electricity bill. This payment is sometimes called a “feed-in tariff.”
The availability of this feed-in tariff is intended to encourage the installation of solar generation capacity in domestic and business premises. This is advantageous as a matter of public policy because of the reduction of the use of fossil fuels for generation of electricity. Local generation which is aligned to peak usage may also reduce the need to install electricity transmission infrastructure in order to meet peak demand which is unused outside peak periods.
A problem arises in some circumstances due to the fact that solar installations are not directly controlled by the energy utility, either in installation or operation. In some instances this has led to problems with grid stability. Where a significant solar generation capacity exists, uncontrolled, rapid changes in the generation capacity on the grid may occur. The grid operator must adapt to this using the generation and distribution assets which are under the operator's direct control. As the amount of solar generation increase, this may become difficult or impossible.
Some energy utilities have reacted to this by requiring that solar installations either do not feed-in any electricity to the grid, or that they make no net feed-in over a specified period.
In general, existing solar installations do not have the capacity to determine or act upon the energy demand of the premises in which they are installed.